Pulse-echo system for indicating angles



May 9, 1959 w. D. HERSHBERGER 2,56,?85

PULSE-ECHO SYSTEM FOR INDICATING ANGLES Original Filed Nov. 2, 1942 5 Sheets-Sheet 1 IN V EN TOR.

May 9, EQSQ W. D. HERSHBERGER PULSE-ECHO SYSTEM FOR INDICATING ANGLES 3 Sheets-Sheet 2 Original Filed Nov. 2, 1942 Q J 2 6 WW7 i EM v [7i i M a v AMW R umw vmi y 9 195$ w. D. HERSHBERGER 2,56,785

PULSE-ECHO SYSTEM FOR INDICATING ANGLES Original Filed Nov. 2, 1942 s sheets-sheet s Patented May 9, 1950 2,506,785 PULSE-ECHO SYSTEM FOR INDICATING ANGLES William D. Hershberger, Princeton,-.N. J.-, assignoif to Itadiofllorporation of America, a corporation of Delaware Original application November 2, 1942, SerialNo'. 464,291, now Patent No. 2,430,292, dated-Novem: ber4; 1947. Divided and this application December 29, 1944, Serial No. 570,266

5 Claims.

. 1 V This application is a division of my copending United States application Serial No. 464,291, filed November 2, 1942, entitled Radio angle indicator, now Patent 2,430,292 issued November 4, 1947. My invention relates to radio-echo or similar systems for angle measurements and particularly to a radio system for measuring angles such as the angle formed by a line from an aircraft to an object on the earths surface and apei'pem dicular line from the aircraft to earth. The object may be a ship or other target to be bombed from the aircraft.

a An object of the invention is to provide an improved method of and means for measuring an angle between lines joining a point of signal radiation and two points on a surface where one of the other angles of the triangle formed by said lines and a line between said two points on ;said surface is a fixed known angle.

A further object of the invention is to provide ;an improved system of the above-described type for determining the said angle between the'per- -pendic'ular and the line to the target or other ,reflecting surface.

A further object of the invention is a provide :an improved system in which measurementjof the said angle is independent of the attitude of :aircraft.

A further object of theinvention is to provide :an improved sy'stem'of' the above-described type for determining the said angle even though the" .shipor other target is not visible;

A further object of the invention s it prov d :an improved system of the above-described type .in which the angle measurement may be read directly from a scale orthe like. V z I Astill further Object Of the invention is" t5] "f0: vide an improved system for landing of aircraft by instruments. v In one preferred embodiment of the invention, an aircraft is provided with. a radio pulser-echd system which radiates aisignal downward arid forward whereby reflections that area measure of altitude will'be received from the earth directly belowth'e plane while other reflections'will be received from the target ahead. I Sincethe first occurring refiectionslwill bea measure of the altitude or distance perpendicular to the earth, the angle 0' between this perpendicular line and the line from the aircraft to the target can' be determined when the range or distance to the target is also known. The latter distance is shown by a later occurring reflection from the target. From the fact that the distance to the target divided by the altitude is the secant of the angle 0, the angle 0 may be calculated. In accordance with my invention, however, the auparatus isso designed thatthe angle b is read directly off a scalewithout the necessity of any calculations.

, This may be accomplished in accordance with my invention by'causiri'g the cathode ray of the indicatortu'beto be deflected alternately along two deflectionpaths or traces, one of them being ayertical trace produced by a sawthooth wave on the vertical deflecting plates only and the other being a trace 'positionedat an angle with respect to the'v'ertical trace and produced by applying the'sawtoo'th to both the vertical 'and'the horizontal deflecting plates. The altitude and target pulse indications appear on these traces. ihe desired angle (9' (Fig. 2') may be determined by keeping the twotraces of equal length and by making the angle (Fig. 3)' between them such that the 'targ'et'pulse indication on the angularly located trace and the altitude pulse indication on the vertical trace'fall on the same horizontal line, i.'e.,.by' making them horizontally coincident. The angle between the two traces is now equal to the desired angle 0 and may be read from an angle scale marked on the face of the indicator tube. Other embodiments of the invention will be described hereinafter.

The invention will be better understood from the following. descriptiontaken in connection with the accompanying drawing in which t Figure 1 is a, blockvandcircuit diagram showso e mb d m n of t i v nt Figure 2 is adiagram showing the relation between the altitude echo path, the target echo path and the angle 0, I

Figure} is a view representing the screen'- end of the indicator tubefof Fi'g. 1 with cathode ray trajces' and pu1se,,injdications thereon as they appear when utilizing the embodiment of Fig. l,

Figure4 is a diagram illustrating the desired glide path for an airplane of a particular type in makingalandin'g, I v

Figure 15 is a view which is the same as that of'Fig'. 3 except that it illustrates the traces" and pulse indications for the condition when the system of Fig. 1 is employed for making an instrument landing,

Figure 6 is a block and circuit diagram illustrating another embodiment of the invention that is particularly adapted for use in making instrument landings,

Figure '7 is a view representing the screen end of the indicator tube of Fig. 6 with the cathode ray traces and pulse indications thereon, and

Figure 8 is a pair of graphs showing how leftright indication is applied to the system of Fig. 6.

In the several figures, like parts are indicated by similar reference characters.

In Fig. 1, a high frequency radio transmitter 10, which is mounted on an aircraft l2 (Fig. 2)

is keyed by means of a pulse keyer it connected to a keying pulse generator l4 through a delay network IE to radiate short radio pulses downward and forward from a suitable antenna system I 6, which is illustrated as a dipole in a parabolic reflector. The transmitted pulses may occur at a rate of 3500 per second and have a duration of 0.3 microsecond, for example.

The reflected or echo pulses are picked up by a suitable antenna such as a dipole 2i and supplied to a receiver 22 (also on the aircraft) which amplifies and demodulates them. They are further amplified by an amplifier 23 and applied through a coupling capacitor to a pair of horizontal deflecting elements 2'! and 270, of a cathode ray indicator tube 29. The cathode ray tube 29 may be of conventional design and is provided with a pair of vertical deflecting elements 35 and 31a positioned at right angles to the other pair of elements.

A deflecting voltage generator 36 supplies a linear sawtooth voltage across an output resistor 31. This deflecting voltage is applied in the mann-er described below through manually adjustable potentiometers 3838a, 39 and ll to the deflecting elements of tube 29. The sawtooth generator 36 is synchronized with the pulse transmission by means of pulses from the pulse generator is supplied thereto through a conductor 42, an amplifier 43 and a conductor 44. r

The upper end of resistor 38 of the gain control potentiometer 3838a is connected through a relay armature 46' either to an intermediate point on resistor 3? or to the upper end of resistor 37, the first position being for the operation when measuring angles as illustrated in Fig. 3. It is only for blind landing operation or the like that a switch 41 is closed whereby the armature 46 is pulled periodically into contact with the upper end of resistor 31 by a relay coil 48. Such periodic operation of the armature 46, with the resulting'periodic change in magnitude of cathode ray deflection is obtained by means of a cam operated switch driven by a motor 52.

The lower end of resistor 38 is connected through a variable tap 53 to a point on the resistor 38a which is connected at each end through ground to the lower end of output resistor 31. Moving the tap 53 in either direction from the center position results in a reduction in the amplitude of the deflecting voltage applied to potentiometer resistors 39 and 4| since the relative circuit impedances are such that there is substantially no change in the current flow through the resistors 38 and 38a resulting from a change in the position of the tap 53. Opposite ends of resistors 39 and 4|, respectively, are connected through a resistor 54 to a point on resistor 38.

4 The other ends of resistors 39 and M are grounded.

Horizontal deflecting voltage is supplied periodically from resistor 4| to the deflecting elements 21-2'ia through a variable tap 55 and a relay armature 57. Vertical deflecting voltage is supplied from resistor 39 to the vertical deflecting elements 3 l--3Ia through a variable tap 58 and a relay armature 59, this voltage being supplied alternately with reduced amplitude (depending on the position of tap 58) and with full amplitude. When it is supplied with full amplitude, the armature 59 is in its lower position and the armature 51 is disconnected from the horizontal deflection supply whereby the vertical deflection trace 6% (Figs. 1 and 3) is produced.

During the instant that the vertical deflection voltage is supplied with less than full amplitude, the armatures 5e and 57 are in their upper positions and the cathode ray is being deflected both vertically and horizontally by amounts determined by the positions of the taps 53, and 53 which are gangedtogether for manual adjustment by operating a control knob 62 as indicated by the broken lines. This simultaneous vertical and horizontal deflection produces the trace 63 (Figs. 1 and 3). The armatures '59 and 51 are actuated by means of relay coils 64 and 66, respectively, which are energized periodically and simultaneously by the closing of the cam operated switch 5!.

When the taps 53 and 56 are positioned at points where the vertical and horizontal voltages are equal, the trace 63 is at 45 degrees with respect to the vertical trace El and is of minimum length for a given amplitude of deflecting voltage.

Therefore, when taps 58 and 56 are so positioned, the tap 53 is positioned at the center of resistor 38a, this being its position for maximum voltage. If the control knob 62 is turned to move the taps 56 and 53 to the right of the above-mentioned equal-voltage position, the vertical deflection is decreased in amplitude and the horizontal deflection is increased in amplitude whereby the trace 63 swings away from the vertical trace 6!.

- Simultaneously, the tap 53 moves to the right to decrease the amplitude of the deflecting voltage by the correct amount for keeping the length of the trace unchanged. Likewise, if the taps 55, 58 and 53 are moved to the left of said position the trace 63 swings toward the vertical trace (it. As before, its length does not change. In order to make the amplitude of the deflecting voltage decrease in the desired manner as the tap 53 is moved, it may be desirable to have the resistance of resistor 38a tapered instead of having it change linearly with respect to the position of the tap The cam switch 5| preferably is closed periodically at a rate that is high enough to make the traces BI and 63 appear to an observer to be on the cathode ray screen at the same time.

In order to determine the angle 0 between the vertical and the line of sight to a target (Fig. 2) the potentiometer knob 52 is adjusted until the angular trace 63 is swung through such an angle that the target echo pulse indication T thereon and the altitude echo pulse indication A of the vertical trace 5! are horizontally coincident, as shown in Fig. 3. The condition of horizontal coincidence is obtained when the above-men-v tioned indications T and A fall on the same horizontal line such as one of a plurality of lines (51 marked on the face of the tube 29. The angle 4; now equals the angle 0 and its value may be read at the point as on an angle scale 68 where the endxof trace tt-fallsoncr: adjacent to the: angle?- scale; Thereasonzthatlthe above-describediprocedure givesthedesired angle isthatithe geometry of the two cathode-ray traces 61 and-63and thehorizontaliline of Coincidence correspond exactly-to the geom'etry of the altitude, target dis.- tance andground level, respectively, indicated in Fig.- 2.

My system' may be employed for instrument landings of airplanes if the landing field is pro vided with a marker such asareflectoror retransmitter to-givethe pulse-echo indication T. For example; an airplane equipped with my 'system canbe brought into a landing field alonga straight line glide path if-"the pilot will keep his altitude such that the altitude andmarker indications A and v T, respectively, remain hor-i-- zontally coincident;

Some pilots prefer changing the angle of theglide path: during alanding asshown, by way otexample, in Fig. 4; An airplane maybe landed inthis way with my :system and without adjusting the control knob 62. if the switch 41 (Fig; 1) isclosed. This pulls the armature 46 against its right-hand contactpoint whereby the deflectingrvoltageis ofv increased amplitude during the time the cathode .ray. iszdeflected vertically. along the. trace "H (Fig.1 5). This: gives the vertical trace an. expanded scale; which is desirable" because ofrthe low-altitude.- of: the. airplane during landing. The altitudeindication A and the target or marker indication Tappear on the useful lengths ofzthetracesfl l 1 andi'l2, respectively. The target or marker. pulse: T. may not appear on'the trace H (although it always appears ontrace 12) or it may appear on'trace 'H- onlywhen the landing is substantially completed; The altitude indicationA will not appear on the useful portion of-trace 12; instead it will be near the-upper end of the trace 72 or may not evenbe visibleon trace '12 (although it always appears on trace 1!). A- plurality of. lines such as m, n, o and 11 may bedrawn across-the face of the tube 29 to intersect the traces H and 12 at the points where the pulse indications A and T, respectively, will fall-if the airplane is coming in at the: desired glide. angle.

For example, at4000' from'the marker '(Fig. 4) thezpilot has dropped'to an altitude of 500"where the proper glide angle-is indicated by the 72 line m. It shouldbenoted that 7.2 is the value of the-'anglea-(Fig. 4') rather. than the value of theglidetangle itself. The 'airplane'may be held at the indicated glide angle until pointZ (Fig.4) ismeacned, at which point the angle-may be changed to that indicated by the 5.7 line it: Similarly, the glide angle may be changed at other predetermined altitudes as the airplane approaches the runway. In practice, a pilot would probably change the glide angle gradually, watching the altitude and marker indications tosee that the altitude and marker indications A and T, respectively, are approaching the index 'li'nes m"; n, 0, etc. in the proper manner.

Fig. 6 illustrates: another-embodiment of the invention which is designed particularly for the instrument landing" of aircraft. In this embodiment, the sawtooth deflecting voltage is applied tothe vertical defiectingplates 3| and 3la only. The simultaneous application of centering voltages results in theproduction of vertical traces TB and Ti as shown in Fig. '7. Just asin Fig. 5, the trace '76 for indicating altitude has an ex panded scale.

the .saw-toothadeflecting:voltage to.-the defiecting.-

plates 3.! and;=.3 l a. throughione of the two; contact; points 18: andv I9: and? a .relay' armature 8 l The armature" 8 I. is=pulledfrom one contact. point to. the otherby arelaycoil. 82 that, is energize'dby axswitch 83. Thesw-itch'83. is operated by'a cam 8t which is driven 'by the motor '52-.

When the armature 281' is in the position shown for producingthe expanded scale trace l5,:a:posltive centering voltage is applied to the deflecting plate 21 through. azrelay armature 86 andaresister 81. This pulls the vertical deflection to; one-side-of centen Whenthe armature BI is in the otherposition for applying a deflecting voltage of smaller amplitude, thus' producing the trace ll the armature 8'6 isin its other position to applya negative" bias to the deflecting plate 21-; This pulls the vertical deflection to the other side of center. The-armature 86 isactuatedin synchronism withthe--- armature Bl by a relay coil 88.

The operation of'the system is similar to that described'in connection with Fig. 5. A plurality of lines suchas d, eand f are'drawn across the face ofthe tube 29-'to intersect the traces'lt and H at the points where the 'altitude'anditarget (marker) pulses'A and T; respectively; appear when the airplane is on the desired glide path- Preferably, the. system of Fig. 6 includesleftright indication. This may be providedby'supplying the output of transmitter"! through a left-rightswitchingjdevice 89'to a pair of directional antennas. 9 l' and'f92. having overlapping radiation. patterns. Switching device 89 is. driven by the motor 52fwhich also drives the cam operated switches 93 and. 94. Switches 93 and 94' control a pair of relayv armatures 96 and 91; respectively, to apply the echo pulses alternately to the horizontal deflectingv plates 2'i'a and 21, respectively. Thus, the cathode .ray is deflected. to the left by the .echo pulsewhen the radiation is fromthe antennahaving the left-hand radiation. pattern and it is defiected to the right when the radiation is from the other antenna. When the airplane onWhich-the system is mounted is headeddirectly-for the landingfield marker, the, left and'right defiections -are-of-the same amplitude and the pilot knows he is: approaching the runwaycorrectly. This conditionisillustrated at A and T in Fig." 7.

One satisfactory switching sequence is illustrated in Fig. 8 whereleft and right switching periods are'shown atLan'd R. The corresponding switching periods-to produce the altitude and range or. marker traces l6 and TI are. shown at alt. and range, respectively. It will be seen that one altitude traceJfi-andone range trace 11'- are' produced whilesignalis radiated toward the left. These two'traoes-are again produced While signal. is being radiated toward the right. It will be'understood thatthe rate of switching is not critical but with. a given cathode ray tube screen having a. certain persistence of fluorescence it shouldb'e high. enough to make the altitude and: range traces visible simultaneously without too muchfl'icker.

Iclaim as my invention:

1. In a system-for 'indicating on the screen of a catno'de ray tube the angle between a line from an aircraft to a finite object on the earths-sui face and a-line perpendicular from the aircraft to the earthjthe earth s-surfac'e being level-from the point: where said perpendicular line strikes'said The traces lit-and are obtained by applying surfaceito; said.object.la cathoderay tube havingv a screen and having means for producing a oathode ray and directing it at said screen, means for transmitting radio pulses toward the earth from said aircraft and for initiating alternately at approximately the time of transmission of each pulse a deflection of the cathode ray to produce a certain time trace on said screen and a deflection of the cathode ray along a different path to produce a time trace on said screen spaced away from said certain trace and in a fixed relation thereto, said time traces having time bases that have a predetermined relation to each other, means for receiving said pulses after reflection from said surface and from said object, means for applying the received pulses to said tube to alter the cathode ray during its deflection to produce a visual indication whereby the altitude indication appears on one trace and the object indication appears on the other trace, and a plurality of lines drawn over said screen to intersect said traces, each line intersecting one trace where the altitude indication appears for a certain altitude and intersecting the other trace where the object indication appears for a certain value of said angle.

2. In a system for indicating on the screen of a cathode ray tube the angle between a line from an aircraft to a finite object on the earths surface and a line perpendicular from the aircraft to the earth, the earths surface being level from the point where said perpendicular line strikes said surface to said object, a cathode ray tube having a screen and having means for producing a cathode ray and directing it at said screen, means for transmitting radio pulses toward the earth from said aircraft and for initiating alternately at approximately the time of transmission of each pulse a vertical deflection of the cathode ray to produce a vertical time trace on said screen and a horizontally displaced vertical deflection of the cathode ray to produce a second vertical time trace on said screen, said time traces having time bases that have a predetermined relation to each other, means for receiving said pulses after reflection from said surface and said object, means for applying the received pulses to said tube to alter the cathode ray during its deflection to produce a visual indication whereby the altitude indication appears on the first trace and the object indication appears on the second trace, and an index line drawn over said screen to intersect the first trace where the altitude indication appears for a certain altitude and to intersect the other trace where the object indication appears for a certain value of said angle.

3. In a system for indicating on the screen of a cathode ray tube the angle between a line from an aircraft to a finite object on the earths surface and a line perpendicular from the aircraft to the earth, the earths surface being level from the point where said perpendicular line strikes said surface to said object, a cathode ray tube having a screen and having means for producing a cathode ray and directing it at said screen, means for transmitting radio pulses toward the earth from said aircraft and for initiating alternately at approximately the time of transmission of each pulse a vertical deflection of the cathode ray to produce a vertical time trace on said screen and a horizontally displaced vertical deflection of the cathode ray to produce a second vertical time trace on said screen with the rate of movement of the cathode ray along the first trace being substantially faster than along the second trace, said time traces having time bases that have a predetermined relation to each other, means for receiving said pulses after reflection from said surface and from said object, means for applying the received pulses to said tube to alter the oathode ray during its deflection to produce a visual indication whereby the altitude indication appears on the first trace and the object indication appears on the second trace, and an index line drawn over said screen to intersect the first trace where the altitude indication appears for a certain altitude and to intersect the other trace where the object indication appears for a value of said angle.

4. In a system for indicating on the screen of a cathode ray tube the angle between a line from an aircraft to a finite object on the earths surface and a line perpendicular from the aircraft to the earth, the earths surface being level from the point where said perpendicular line strikes said surface to said object, a cathode ray tube having a screen and having means for producing a cathode ray and directing it at said screen, means for transmitting radio pulses toward the earth from said aircraft and for initiating alternately at approximately the time of transmission of each pulse a vertical deflection of the cathode ray to produce a vertical time trace on said screen and a horizontally displaced vertical deflection of the cathode ray to produce a second vertical time trace on said screen with the rate of movement of the cathode ray along the first trace being substantially faster than along the second trace, said time traces having time bases that have a predetermined relation to each other, means for receiving said pulses after reflection from said surface and from said object, means for applying the received pulses to said tube to alter the cathode ray during its deflection to produce a visual indication whereby the altitude indication appears on the first trace and the object indication appears on the second trace, and a plurality of index lines drawn over said screen to intersect said traces, each line intersecting the first trace where the altitude indication appears for a certain altitude and intersecting the other trace where the object indication appears for a certain value of said angle.

5. In a system for indicating on the screen of a cathode ray tube the angle between a line from an aircraft to a finite object on the earths surface and a line perpendicular from the aircraft to the earth, the earths surface being level from the point where said perpendicular line strikes said surface to said object, a cathode ray tube having a screen and having means for producing a cathode ray and directing it at said screen, means for transmitting radio pulses toward the earth from said aircraft in left-right overlapping radiation patterns and for initiating alternately at approximately the time of transmission of each pulse a vertical deflection of the cathode ray to produce a vertical time trace on said screen and a horizontally displaced vertical deflection of the cathode ray to produce a second vertical time trace on said screen, said time traces having time bases that have a predetermined relation to each other, means for receiving said pulses after reflection from said surface and from said object, means for applying the received pulses to said tube to alter the cathode ray during its deflection to produce a visual indication whereby at least the altitude indication appears on the first trace and at least the object indication appears on the second trace, a plurality of index lines drawn over said screen to intersect said traces, each line intersecting the first trace where the altitude indication appears for a certain altitude and intercertain secting the other trace where the object indication appears for a certain value of said angle, and switching means for producing said first and second vertical traces during pulse transmission in the left radiation pattern and for next producing them during pulse transmission in the right radiation pattern.

WILLIAM D. HERSHBERGER.

REFERENCES CITED Number UNITED STATES PATENTS Name Date Bowyer June 14, 1887 Hammond et a1 Mar. '7, 1922 Dugan Apr. 14, 1931 Somers et a1 Oct. 6, 1936 Zworykin Dec. 19, 1939 Hershloerger Feb. 6, 1940 Hunter Dec. 17, 1940 Hardy May 21, 1946 Newhouse Aug. 6, 1946 Wolff Dec. 17, 1946 

